1. Field of the Invention
The present invention relates to asphalt-based roofing materials such as shingles and processes for the manufacture of asphalt-based roofing materials.
2. Brief Description of the Prior Art
Asphalt-based roofing materials are ubiquitous in North America. Typically, these materials take the form of sheets or shingles which include a fibrous web embedded in a layer of a bituminous, asphalt-based composition to form a membrane which provides water resistance. Mineral-based granules are typically adhered to the exposed portions of the upper side of the sheet or shingle to provide a desirable aesthetic effect and to protect the underlying asphalt-based composition from harmful ultraviolet radiation.
It is important to ensure that the roofing granules adhere to the asphalt substrate during the life of a shingle as it exposed to outdoor environments. However, adhesion of the roofing granules can be disrupted by impact forces, particularly those arising from hail storms. As a result, asphalt shingles can suffer from excessive granule loss due to the impact damage of hail or other projectiles. This not only can cause undesirable appearance of black spots on the roof, but also can result in premature failure in shingles by exposing the underlying asphalt to harmful UV radiation.
Also, some shingles or roofing membranes may suffer from cracking or puncture damage during an extreme severe hail storm. This can result in leaking or further water damage to the roof assembly or interior of a house. Thus, it is advantageous to have asphalt shingles with increased resistance to damages due to impact events.
Improved impact resistance is disclosed in U.S. Pat. No. 6,426,309 for asphalt-based roofing materials which include a protective coating adhered to the upper surface of the asphalt coating, a layer of granules adhered to the protective coating, and a web bonded to the lower region of the asphalt coating. The impact resistance of these roofing materials is improved, as the protective coating is disclosed to prevent excessive granule loss while the web is disclosed to act to stop crack propagation.
A wind-resistant shingle and a method of making it is disclosed in U.S. Pat. No. 6,758,019 in which the rear surface of the shingle is provided with an attached reinforcement layer, which resists upwardly wind-applied bending torque when the shingle is installed on a roof, such that the failure of the shingle when it is bent beyond its elastic limit, is resisted until the shingle has absorbed a high percentage of applied torque.
A method of repairing cracks in a paved asphaltic surface is disclosed by U.S. Pat. No. 7,059,800. A layer of liquefied asphalt is applied to a cracked, paved surface, and a reinforcement mat is then applied over the liquefied asphalt, which penetrates and soaks the reinforcement mat to form a water barrier. Finally, a layer of paving material is applied over the mat. Although it is known to apply a surface coating onto a roof after the roofing shingles have been installed to protect the shingles from granule loss and other damage, such surface coatings can be expensive and require additional labor to apply after the roofing shingles have been installed.
Improved granule adhesion is disclosed in U.S. Pat. No. 7,125,601. An integrated granule product includes a film having a plurality of ceramic coated granules bonded to the film by a cured adhesive. The film can then be applied over a roofing substrate. For example, the integrated granule product can be applied onto an asphalt-based substrate to form a roofing shingle.
There is a continuing need to extend the effective service life of roofs surfaced with asphalt-based roofing materials, and in particular to extend the life of roofs experiencing impact damage from hail and like circumstances.